Pierce the sweet potatoes with a fork. Microwave on HIGH for 8 to 13 minutes or bake at 400°F. for 1 hour or until they're fork-tender. Cut in half lengthwise. Scoop out potato pulp and set aside.
Heat the butter in a 6-quart saucepot over medium heat. Add the onion and celery to the saucepot and cook until they're tender. Add the broth and potato. Heat to a boil. Reduce the heat to low and cook for 15 minutes or until the potato is tender. Add the maple syrup, white pepper and reserved sweet potato.
Place one third of the broth mixture into a blender or food processor. Cover and blend until smooth. Pour the mixture into a large bowl. Repeat the blending process twice more with the remaining broth mixture. Return all of the puréed mixture to the saucepot. Add the cream, if desired. Cook over medium heat until the mixture is hot. Season to taste.